I've worn out a half dozen hammocks on my boat.  Mainly because I particularly favor the Mexican variety made of cotton so they eventually rot.

I rig my hammock on the boom.  I have a nylon strap with 2 D rings that I slip between the mainsail and boom.   I then clip a carabiner to the D rings and that holds one end of the hammock.  The other end is held by a carabiner clipped to the bail on the end of the boom.

I have to open the companionway slide all the way so I can hang in the opening of the companionway. Works out great because I can then use the cabin top as sort of a table for drinks, books, laptops, etc.  It's almost like sitting in an easy chair.

Actually it is not hard to 'dismount' at all.  Essentially my entire body is hanging in the companionway such that I can place a pillow on the (fully retracted) hatch slide for my head. Thus my rump is hanging just outside the companionway and my legs/feet extend over the cockpit well.

I suspect the particular length & design of the (Mexican) hammock that allows this particular rigging.  Not sure if other hammocks would fit properly.

I've never been that successful hanging it fwd (between mast & staysail stay).  It tends to develop some kind of 'sympathetic oscillation'.  A friend of mine hung one of those hanging hammock chairs on the stay and in minutes he was swinging almost outside the caprails every time he tried sitting in it.  I thought about maybe charging a fee for the amusement ride.